linux-kernel - Re: [PATCH 2/3] mm/slub: wrap cpu_slab->partial in CONFIG_SLUB_CPU

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Date:   Sun, 30 Apr 2017 19:41:03 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Wei Yang <richard.weiyang@...il.com>
Cc:     cl@...ux.com, penberg@...nel.org, rientjes@...gle.com,
        iamjoonsoo.kim@....com, akpm@...ux-foundation.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] mm/slub: wrap cpu_slab->partial in
 CONFIG_SLUB_CPU_PARTIAL

On Sun, Apr 30, 2017 at 07:31:51PM +0800, Wei Yang wrote:
> @@ -2302,7 +2302,11 @@ static bool has_cpu_slab(int cpu, void *info)
>  	struct kmem_cache *s = info;
>  	struct kmem_cache_cpu *c = per_cpu_ptr(s->cpu_slab, cpu);
>  
> -	return c->page || c->partial;
> +	return c->page
> +#ifdef CONFIG_SLUB_CPU_PARTIAL
> +		|| c->partial
> +#endif
> +		;
>  }

No.  No way.  This is disgusting.

The right way to do this is to create an accessor like this:

#ifdef CONFIG_SLUB_CPU_PARTIAL
#define slub_cpu_partial(c)	((c)->partial)
#else
#define slub_cpu_partial(c)	0
#endif

And then the above becomes:

-	return c->page || c->partial;
+	return c->page || slub_cpu_partial(c);

All the other ifdefs go away, apart from these two:

> @@ -4980,6 +4990,7 @@ static ssize_t objects_partial_show(struct kmem_cache *s, char *buf)
>  }
>  SLAB_ATTR_RO(objects_partial);
>  
> +#ifdef CONFIG_SLUB_CPU_PARTIAL
>  static ssize_t slabs_cpu_partial_show(struct kmem_cache *s, char *buf)
>  {
>  	int objects = 0;
> @@ -5010,6 +5021,7 @@ static ssize_t slabs_cpu_partial_show(struct kmem_cache *s, char *buf)
>  	return len + sprintf(buf + len, "\n");
>  }
>  SLAB_ATTR_RO(slabs_cpu_partial);
> +#endif
>  
>  static ssize_t reclaim_account_show(struct kmem_cache *s, char *buf)
>  {
> @@ -5364,7 +5376,9 @@ static struct attribute *slab_attrs[] = {
>  	&destroy_by_rcu_attr.attr,
>  	&shrink_attr.attr,
>  	&reserved_attr.attr,
> +#ifdef CONFIG_SLUB_CPU_PARTIAL
>  	&slabs_cpu_partial_attr.attr,
> +#endif
>  #ifdef CONFIG_SLUB_DEBUG
>  	&total_objects_attr.attr,
>  	&slabs_attr.attr,